1. Field of the Invention
The present invention relates to a laser power controlling method and apparatus for a semiconductor laser, and a recording/reproducing method and apparatus for a magneto-optical recording medium, and a recording/reproducing method and apparatus for an optical recording medium.
2. Description of the Related Art
A conventional example of a semiconductor laser driving circuit will be explained with reference to FIG. 6. In FIG. 6, SL designates a high-output purple color semiconductor laser [GaN-based semiconductor laser (laser diode)] while DSL designates a drive circuit for driving the semiconductor laser SL. Hereinafter, a detailed explanation will now be given of the drive circuit for driving this semiconductor laser with reference to a timing chart of FIG. 7 as well. It is to be noted that the timing charts of FIG. 7 are illustrated considering a case where the semiconductor laser SL is used in an optical head as later described of the optical disk recording/reproducing apparatus (recording/reproducing method).
This drive circuit DSL is constructed of a switch-equipped current source circuit SIK and an output transistor Qb. The switch-equipped current source circuit SIK is constructed of a switch transistor (for example, an NPN type transistor) Qa, a current source IS, and resistors R10, R11 and R12. The output transistor Qb is constructed of, for example, a PNP type transistor.
The emitter of the transistor Qa is grounded, and the base thereof is grounded via a base-biasing resistor R11. The collector of the transistor Qa is connected to a power source of Vcc=10V via the current source IS and the resistor R10. A point of connection between the current source IS and the resistor R10 is connected to the base of the transistor Qb. The emitter of the transistor Qb is connected to the power source of Vcc=10V while the collector thereof is connected to the anode of the semiconductor laser (a laser diode) SL and the cathode thereof is grounded.
A control signal CS from an input terminal T2 is supplied to the base of the transistor Qa via the resistor R12, whereby the transistor Qa is on/off controlled. As illustrated in FIG. 7C, this control signal CS, at the time of recording, changes alternately to “1” and “0” and, at the time of reproduction, is always kept to have a level of “1”. Also, a peak current setting signal CI is supplied to the current source IS from an input terminal T1 and, as illustrated in FIG. 7B, a control is performed such that the peak current Ip at the time of recording becomes larger in amount than the peak current Ip at the time of reproduction. Further, a Vop in each of FIGS. 6 and 7A represents the operating voltage of the semiconductor SL. An Iop in FIG. 6 represents the operating current of the semiconductor laser SL.
The switching transistor Qa, at the time of reproduction, is always kept “on” and, at the time of recording, is turned on/off in correspondence with the recording timing (or in correspondence with the recording data). Accordingly, at the time of reproduction, the operating voltage Vop of the semiconductor laser SL has a constant voltage of, for example, 5.5 V while, at the time of recording, that operating voltage becomes a pulse voltage wherein a level of 7.0 V and a level of approximately OV are alternately repeated. The operating current Iop of the semiconductor laser SL, at the time of reproduction, has a constant value of, for example, 50 mA, and, at the time of recording, has an average current value of, for example, 110 mA.
Incidentally, although there is a case where, at the time of reproduction, with an aim to decrease the noises, a small-amplitude sine wave signal of several hundreds of MHz is superimposed on the operating current lop of the semiconductor laser SL, but since this has no direct relevancy to the operation of the semiconductor laser driving circuit DSL, the illustration is omitted.
Although, in the semiconductor laser driving circuit DSL of FIG. 6, an NPN type transistor is used as the switching transistor Qa of the switch-equipped current source circuit SIK and a PNP type transistor is used as the output transistor Qb, as illustrated in FIG. 8, a PNP type transistor may be used as the switching transistor Qa and an NPN type transistor may be used as the output transistor Qb.
The semiconductor laser driving circuit in that case will now be explained with reference to FIG. 8. Incidentally, in FIG. 8, the relevant explanation will be made with the same reference symbols being used to designate the corresponding portions to those of FIG. 6. This drive circuit DSL is constructed of the switch-equipped current source circuit SIK and the output transistor Qb. The switch-equipped current source circuit SIK is constructed of the switching transistor (PNP type transistor) Qa, current source IS, and resistors R10, R11 and R12. The output transistor Qb is constructed of an NPN type transistor.
The emitter of the transistor Qa is connected to the power source of Vcc=10V, and the base thereof is connected to the power source of Vcc=10V via the base-biasing resistor R11. The collector of the transistor Qa is grounded via the current source IS and the resistor R10. The connection point between the current source IS and the resistor R10 is connected to the base of the transistor Qb. The emitter of the transistor Qb is grounded while the collector thereof is connected to the cathode of the semiconductor laser (a laser diode) SL and the anode thereof is connected to the power source of Vcc=10V.
From the input terminal T2 the control signal CS is supplied to the base of the transistor Qa via the resistor R12, whereby the transistor Qa is on/off controlled. This control signal CS, at the time of recording, changes alternately to “1” and “0” and at the time of reproduction, is always kept to have a level of “0”. Further, from the input terminal T1 the peak current setting signal CI is supplied to the current source IS and a control is performed such that the peak current Ip at the time of recording becomes larger in amount than the peak current Ip at the time of reproduction. The Vop represents the operating voltage of the semiconductor SL. The Iop represents the operating current of the semiconductor laser SL.
For example, the drive circuit for driving the semiconductor laser in FIG. 6 will be described below. The power consumption P of the output transistor Qb is expressed by the following equation (1).P=(Vcc−Vop)×Iop  (1)
Calculating by substituting Vcc=V10V, Vop=5.5 V (minimum value), and Iop=110 mA (maximum value) into the equation (1) above, the power consumption P of the output transistor Qb is expressed as done by the following equation (2).P=(10−5.5)V×110 mA=495 mW  (2)
For example, in case of a red color semiconductor laser, calculating by substituting Vcc=5V, Vop=1.8 V (minimum value), and Iop=120 mA (maximum value) into the equation (1) above, the power consumption P of the output transistor Qb is expressed as done by the following equation (3).P=(5−1.8)V×110 mA=352 mA  (3)
Namely, the power consumption P of the output transistor Qb is small compared with the high-output purple semiconductor laser.
As apparent from the foregoing, since the power consumption of the output transistor Qb in the case where the high-output purple semiconductor laser is used becomes fairly high compared with the power consumption of the output transistor Qb in the case where the red color semiconductor laser is used, it is necessary that a large-sized heat radiator should be attached to the output transistor Qb. However, since the drive circuit for the semiconductor laser is incorporated into the optical head (optical pick-up) jointly with the semiconductor laser, if providing a radiator on the output transistor Qb, the optical head (optical pick-up) inconveniently becomes large in size. However, if a large-sized radiator is not provided on the output transistor Qb, this output transistor Qb generates heat, which shortens the service life of the optical head (optical pick-up) and that of the semiconductor laser.
In view of the above-described points in problem, the present invention is intended to propose a laser power controlling method and apparatus for a semiconductor laser, the method and apparatus being arranged to control the laser power of a semiconductor laser by applying a power source voltage to a serial circuit of a path between the collector and emitter of the output transistor and a semiconductor laser, in which the power consumption of the output transistor can be decreased
Also, the present invention is intended to propose a recording/reproducing method for a magneto-optical recording medium, in which a convergent laser light based on a laser light from a semiconductor laser is irradiated onto a magneto-optical recording medium to heat the same; a magnetic field based on recording information is applied to the heated portion of the magneto-optical recording medium to thereby record the information into the heated portion thereof; and a convergent laser light based on a laser light from the semiconductor laser is irradiated onto the magneto-optical recording medium having the information recorded therein to thereby reproduce the information by using the laser light emitted from the magneto-optical recording medium having the information recorded therein, whereby a power source voltage is applied to a serial circuit of a path between the collector and emitter of the output transistor and a semiconductor laser to thereby control the laser power of the semiconductor laser, the recording/reproducing method thereby enabling decreasing the power consumption of the output transistor.
Further, the present invention is intended to propose a recording/reproducing apparatus for a magneto-optical recording medium which includes an optical head that emits a convergent laser light based on a laser light from a semiconductor laser and magnetic field generator means that applies a magnetic field based on recording information to a magneto-optical recording medium; the convergent laser light from the optical head is irradiated onto the magneto-optical recording medium to heat the same and the magnetic field from the magnetic field generator means is applied to the heated portion of the magneto-optical recording medium to thereby record the information; and a convergent laser light from the optical head is irradiated onto the magneto-optical recording medium having the information recorded therein to thereby obtain from the optical head a reproduction information signal based on an emitted laser light from the magneto-optical recording medium having the information recorded therein, whereby a power source voltage is applied to a serial circuit of a portion between the collector and emitter of an output transistor and the semiconductor laser to thereby control the laser power of the semiconductor laser, thereby enabling decreasing the power consumption of the output transistor.
Further, the present invention is intended to propose a recording/reproducing method for an optical recording medium, in which a convergent laser light, based on a laser light from a semiconductor laser, which is optically modulated by information is irradiated onto an optical recording medium to thereby record the information; a convergent laser light based on a laser light from the semiconductor laser is irradiated onto the optical recording medium having the information recorded therein to thereby reproduce the information in accordance with an emitted laser light from the optical recording medium having the information recorded therein, whereby a power source voltage is applied to a serial circuit of a portion between the collector and emitter of an output transistor and the semiconductor laser to thereby control the laser power of the semiconductor laser, thereby enabling decreasing the power consumption of the output transistor.
Further, the present invention is intended to propose a recording/reproducing apparatus for an optical recording medium which includes an optical head that emits a convergent laser light, based on a laser light from a semiconductor laser, which is optically modulated by information and a convergent laser light which is not optically modulated by information, whereby, by irradiating onto an optical recording medium the convergent laser light of the laser light optically modulated by information from the optical head, the information is recorded and, by irradiating onto the information-recorded optical recording medium the convergent laser light which is not optically modulated by information from the optical head, a reproduction information signal based on the laser light from the information-recorded optical recording medium is obtained from the optical head, to thereby control the laser power of the semiconductor laser, thereby enabling decreasing the power consumption of the output transistor.